the minimod dh-adsr envelope generator is a compact 10hp wide eurorack format module. it has been developed to offer a full adsr envelope for the minimod system and of course other eurorack synthesisers, as
an alternative to the original model d style contour generators which do not have separate decay and release controls.
the dh-adsr uses exactly the same discrete transistor circuitry as the original model d contour generators, so it retains all of the "punchiness" of the original, along with it's unique multiple key trigger
behaviour; we have simply added a release control so that it now offers a true adsr envelope, and the decay and release curves can be individually controlled.

but we have included three exciting new features too:
delay-hold mode which can generate very complex envelopes when mixed with another regular envelope generator output.

retrigger mode which allows automatic re-triggering of the envelope, the pre-delay control sets the "hold off" time between individual retriggers, and the hold control sets the gate length, so it can produce
repeating adsr envelopes, this has a very wide range and even be used as an lfo.

slow mode, this switches the envelope down to 1/5th of regular speed, so slow, evolving envelopes are now possible too.

we have developed this module in response to requests from several existing minimod customers, they really wanted to have full adsr envelopes but still retain the model d envelope characteristics,
particularly its punchy attack and unique multiple key trigger behaviour. so that is exactly what we have done, again we have used exactly the same discrete transistor circuitry and internal voltages as the
original vintage model d and our own minimod contour generator. the changes needed to modify it from the original ads envelope into full adsr are transparent to the circuitry itself, so all of the wonderful
model d character and eccentricities are retained. however we couldn't just stop there, we just had to add some additional, very useful extra features too!

adsr mode
regular adsr envelope mode is selected by setting the slow, retrig and del-hld switches to off (switch up). in this configuration the pre-delay and hold controls have no effect, and a gate will generate a
one shot adsr (attack, decay, sustain, release) envelope. the gate can also be manually triggered using the manual trigger button, which is located just above the release control.

a screen shot of an actual adsr envelope from this module is shown below, note the fast decay and slow release time, this is impossible with the original model d envelope generator, and of course the minimod
dual contour generator too, which shares the same circuitry.

if we try to set up this envelope on the original model d contour generator we get the envelope shown below. here the decay time is set for a fast decay, and we can see that the release time is fast too, as
the decay and release slopes share a single control.

alternatively, if we set the decay control to get the same release time as the adsr example, we get a slow decay time too, as again they share the same control.

multiple key trigger behaviour
there are two factors that make the model d envelope generator unique and contribute considerably towards the sound and appeal of the vintage model d. the first is the "punchiness" of the envelope, they can
be very fast indeed. well, we captured this exactly with our minimod dual contour generator and we are happy to report that our new adsr envelope shares exactly the same speed and contour profiles.

the second distingushing factor is the multiple key trigger behaviour, unlike other envelopes this does not return to zero on multiple fast key presses (or gates), it partially returns and then increases to
a higher level. see the minimod dual contour generator information page for more details on this, suffice it to say here that our new dh-adsr shares exactly the same behaviour, but in addition it can now
accomplish this with a full adsr envelope profile, as can be seen below from an actual oscilloscope screen shot of the dh-adsr in operation, the example here shows multiple key triggers with a fast decay
curve and a slow release curve.

slow mode
slow mode is selected by putting the slow switch to the down position. it slows down the attack, decay and release curves to around 20% of their regular speed, so that long evolving envelopes of well over
one minute in duration are now possible.

the slow mode can be used in all configurations, so it works in adsr, delay-hold and delay-hold + retrigger modes.

del-hld mode
this is delay-hold mode, and is selected by setting the del-hld switch to the down position. now the pre-delay and hold controls become effective and the module works as follows:
when a gate is received (or the manual gate button is pressed) this triggers the pre-delay circuitry, which will delay the start of the envelope, and this "do nothing" time is determined by the setting of
the pre-delay control knob, it can be between 20ms (control fully anticlockwise) and 10 seconds (control fully clockwise)

once the pre-delay cycle is complete the envelope is triggered, and the attack, decay, sustain and release controls work in the same manner as in adsr mode. but there is a difference here, the gate time is
not controlled by the keyboard gate, but instead is controlled by the setting of the hold control, and the gate length can be between 20ms (hold control fully anticlockwise) and 10 seconds (hold control
fully clockwise). having control of the gate length from the hold control instead of the regular key trigger or sequencer supplied gate allow it to generate envelopes that are delayed and different in
length, and one important use of this would be to mix it with a regular envelope to generate a complex envelope which would have an additional attack decay point, two different sustain levels and two
release points.

below is a screenshot from an oscilloscope showing 2 envelopes responding to the same gate signal from a midi to cv converter. at the top we have a dh-adsr envelope generator in regular adsr mode (yellow
trace) and below that trace we have a dh-adsr in del-hold mode (green trace) both received the same keyboard gate, and this illustrates the effect of the pre-delay and hold controls on the dh-adsr. with the
green trace (dh-adsr envelope) it can be seen that although the gate is received at the same time as the adsr module above, the pre-delay control holds off the start of the envelope (in this case for around
800 milli seconds). it can also be seen that the gate length is determined by the hold control setting, not the keyboard gate. here the hold time is set at 1.2 seconds. the purple trace shows the combined,
complex envelope created by mixing the two envelopes together - here for convenience we have used the maths function on the oscilloscope, but in real world situations this can be done rather better with our
minimod cvmix-offset-vca module, which also allow the mix levels to be adjusted and even inverted or offset biased too if desired.

retrigger mode
retrigger mode is selected by setting the retrigger switch to the down position, along with the del-hld switch, which also needs to be on (switch down) as retrigger mode only works with del-hold
enabled.

retrigger is very similar in use to del-hold mode, however when the release curve gets very close to zero the envelope is automatically re-triggered, so the generation of repeating envelopes is now possible.
because we have separate pre-delay and hold controls it is easy to get delayed, repeating envelopes similar to those generated by the ems synthi and vcs3 trapezoid envelope generator, however the dh-adsr has
the further advantage that the envelope shape can be full adsr rather than the simpler attack-hold- release of the ems trapezoid, however ahr envelopes can be easily emulated too by simply setting the
sustain control to maximum.

below is an oscilloscope screenshot of a repeating adsr envelope, created in retrigger mode, here the pre-delay control is set to zero, and you will see that the envelope immediately retriggers at the end of
the previous release curve. the hold control sets the duration of the gate, which commences at the start of the attack curve and ends at the start of the release curve as shown.

next, we can see the effect of adding pre-delay. we have had to change the timebase on the oscilloscope to fit everything in - this is exactly the same envelope as above, but now the added pre-delay creates
a large time delay or "do nothing" period before the envelope retriggers. the pre-delay can be up to 10 seconds, and the hold (gate on) can be up to 10 seconds too, so if we also use a long release time we
can get to almost 30 seconds between repeats, or even longer if we switch the envelope down to slow mode.

we can also use the dh-adsr in retrigger mode as an lfo by using low or zero amounts of pre-delay and hold, below it is shown oscillating at 55hz, it is possible to get it to oscillate at over 100hz, however
this requires careful setting of the controls - at higher speeds the correct envelope shape is important to maintain oscillation. when using ithe dh-adsr as an lfo, the output waveform will be unipolar, 0 to
+8v, however if we pass this through our cvmix-offset-vca module (connect it to channel 3) we can mix a negative bias violtage to it (from channel 1 with no input connected) and we can therefore modify it to
become a bipolar, +/-5v modulation source, with the benefit of a variable adsr envelope shape!

inverted output
in addition to the regular envelope output we have included an inverted envelope output, it is labelled out inv. two different types of envelope inversion are possible, and we have included a jumper on the
rear panel of the module to select between them.

full inversion. this is available with the rear panel jumper removed, the envelope is simply mirrored about the 0 volt axis, and instead of varying between 0 to +8 volts the envelope varies between 0 and -8
volts, as shown below. on the oscilloscope screen capture below the regular envelope is shown in yellow, the inverted envelope is green.

biased inversion. this is available when the rear panel jumper is in place and shorting out the jumper connections.in this case the envelope is not only inverted but also level shifted, so that it
transitions between +8 volts and 0 volts. in this configuration a reverse of the regular envelope is available - this is probably the more useful mode, however we have included both options for completeness.
on the oscilloscope screen capture below the regular envelope is shown in yellow, the biased and inverted envelope is green.

gate
in order to trigger the envelope initially we need a gate, which is a signal that rapidly transitions between ground (zero volts) and +5 volts, and as long as the gate is high the envelope generator will go
through the attack, decay and sustain phases - as soon as the gate is released (returns to zero volts) the envelope generator enters the release phase, and the output will gradually decay down to zero volts
at the rate set by the release control..the usual gate voltage for eurorack systems is +5v, however the dh-adsr will trigger successfully with gate voltages between +2v and +12v. by default the gate signal
from the eurorack power bus is normalised to the dh-adsr gate input jack, so if you are using a midi to cv converter or sequencer that sends a gate to the eurorack bus this will be automatically detected and
used; this is convenient as it cuts down on patching. if an external gate is patched into the gate input this will over rides the gate from the bus, which will then be ignored.

manual trigger button
the manual trigger button is located on the front panel just above the release control knob, and this can be used to manually apply a gate to start the dh-adsr envelope without the need for an external gate.
holding the button down holds the gate open, and releasing the button stops the generation of the gate. so if the button is pressed and held for three seconds, the gate will be three seconds long. the manual
trigger button can be used at the same time as an external gate, for example you may be triggering the envelope using a gate pulse from a sequencer running at 100 bpm, you could press the manual trigger
button between these gates to double up the beat to 200 bpm, always assuming your timing is good :-)

can i use the dh-adsr to replace the minimod dual contour?
yes, of course, and you will gain many extra features too. however two dh-adsr modules will be needed to independantly control (for example) the vcf and vca contour in the same way as the original model d,
because the minimod dual contour has two separate envelope generators, whereas the dh-adsr is a single envelope generator.

if you wish to mimic the limitations of the dual contour generator (and the original model d envelope behaviour) then this can be easily achieved, simply set the decay and release controls to exactly the
same position. to mimic the decay switch(es) being turned off just turn the release control fully anticlockwise, this has exactly the same effect.

we will continue to manufacture and sell the minimod dual contour generator alongside the new dh-adsr envelope, as it is better suited to more compact systems because it takes up only 12hp of rack space. two
dh-adsr modules will require 20hp of rack space, but obviously they offer many extra features such as full adsr, delay-hold mode, retrigger, slow setting and inverted envelopes - now you have a
choice!